You can hardly measure the impact Facebook has on society. Of course, FB and Zuck have their dark side. But people are looking on FB for the people they love for a reason. And hundreds of millions like to use FB in their everyday life - that's why the IPO is so celebrated. FB is now a huge brand.
I firmly believe the social networks - including FB - have a lot to do with the uprisings in the arab world. I think it contributes a lot to make the world flatter, allowing people to live where they want to while staying in contact with their family, former coworkers, etc. It also inspires so many other social tools that allow to transfer knowledge much more efficiently anywhere on earth.
Truth is, FB is still struggling to make money. The banks kept the stock at IPO level with huge bids. But whatever, they brought a fantastic story. And they extracted huge money from the ad market, for sure. But who knows if Zuck will not follow Bill Gates path later?